The present invention relates to a changeover valve and a control cabinet with the changeover valve and a dual gas source gas supply system and more particularly pertains to a changeover valve which attains automatic gas supply switching when the pressure differential of the gas sources at the two sides reaches a predetermined value, and a control cabinet and a dual gas source gas supply system with the changeover valve.
Uninterrupted gas supply is required for gas supply systems in many fields such as the industrial field and medical field. The types and pressure levels of the supplied gas vary. For example, common gas types are oxygen, hydrogen, nitrogen, argon, helium, carbon dioxide gas, ethyne, propane and others. Pressure levels can be categorized into high, medium and low pressures, such as 15 MPa, 10 MPa, 6 MPa, 2.5 MPa, 1.5 MPa and others. To attain uninterrupted gas supply, two gas sources are usually utilized. One of the gas sources is the primary bank and the other is the reserve bank. When the pressure of the primary bank decreases to a predetermined value, the gas source of the gas supply will be switched, i.e. the reserve bank starts to supply gas and becomes the primary bank, and the original primary bank becomes the reserve bank. Uninterrupted gas supply to the output end is attained by repeated switching as above.
There are two operating conditions for switching from one gas source to another, namely semi automatic operation with relief valves at the two sides and automatic operation with relief valves and solenoid valves at the two sides. FIG. 15 shows the gas supply for a common semi automatic operation with relief valves at the two sides. FIG. 16 shows the gas supply for a common automatic operation with relief valves and solenoid valves at the two sides.
As illustrated in FIG. 15, a dual gas source gas supply system comprises: a first gas source 10a and a second gas source 10b, a first relief valve 31a and a second relief valve 31b, a first check valve 32a and a second check valve 32b, a tee union 40 and an outlet relief valve 41. The first gas source 10a comprises one or more than one gas vessels 11a, 12a and 13a connected to a collecting pipe 20a, a shutoff valve 21a and a first filter 22a. The second gas source 10b also comprises one or more than one gas vessels 11b, 12b and 13b connected to a collecting pipe 20b, a shutoff valve 21b and a second filter 22b. The first collecting pipe 20a collects gas from the first gas source 10a which successively passes through the first shutoff valve 21a, the first filter 22a and the first relief valve 31a to attain primary pressure reduction, and thereafter successively passes through the first check valve 32a, the tee union 40 and the outlet relief valve 41 to attain secondary pressure reduction, thereby supplying gas to the output end. Similarly, the second collecting pipe 20b collects gas from the second gas source 10b which successively passes through the second shutoff valve 21b, the second filter 22b and the second relief valve 31b to attain primary pressure reduction, and thereafter successively passes through the second check valve 32b, the tee union 40 and the outlet relief valve 41 to attain secondary pressure reduction, thereby supplying gas to the output end. The difference is that when the two sides are connected to the gas sources, if the first gas source 10a is the primary bank, the output pressure of the first relief valve 31a needs to be manually raised for a certain degree and the output pressure of the second relief valve 31b needs to be manually lowered for a certain degree to become the reserve bank. When the first gas source 10a is used and its pressure level decreases to the output pressure level of the second relief valve 31b, the second gas source 10b starts to supply gas. The first gas source 10a can then be replaced with a new gas source. Before the gas source is replaced, the output pressure of the first relief valve 31a needs to be manually lowered for a certain degree to become the reserve bank. The output pressure of the second relief valve 31b needs to be manually raised for a certain degree to become the primary bank. The check valves prevent backflow of gas when the primary bank and the reserve bank switch between each other. When the requirement for pressure stability of the output pressure of the output end is not high and the usage demand can be fulfilled after the gas pressure is reduced by the first relief valve 31a or the second relief valve 31b, the outlet relief valve 41 can be omitted.
FIG. 16 illustrates a supply system established based on the system shown in FIG. 15, with the addition of a first solenoid valve 33a and a second solenoid valve 33b. A first pressure relay 34a is also installed at the inlet port of the first relief valve 31a and a second pressure relay 34b is installed at the inlet port of the second relief valve 31b. The pressure relays and the solenoid valves are electrically connected through an electric cabinet 35. The first solenoid valve 33a and the second solenoid valve 33b are reverse lockout solenoids so that only one solenoid at one side operates at one time. The pressure setting of the pressure relays is the lowest working pressure of the gas sources. The output pressures of the first relief valve 31a and the second relief valve 31b are the same. When the two sides are connected to the gas sources, a user manually switches on one side to supply gas at the electric cabinet. If the first solenoid valve 33a is connected first, the first gas source 10a is the primary bank, and the second solenoid valve 33b is not connected and the second gas source 10b is the reserve bank. When the first gas source 10a nearly depletes and its pressure decreases to the lowest working pressure of the gas source, the pressure relay 34a is activated and switches off the solenoid valve 33a. The solenoid valve 33b also becomes connected. A signal for gas exchange may also be released to notify the user the need to replace the gas source. The second gas source 10b becomes the primary bank and the first gas source 10a becomes the reserve bank after a new gas source is replaced. This allows switching of gas supply without the need to adjust the output pressure of the first relief valve 31a or the second relief valve 31b. The switching takes places repeatedly to attain automatic gas supply. The check valves prevent backflow of gas after the gas sources deplete. When the requirement for pressure stability of the output pressure of the output end is low and the usage demand can be fulfilled after the gas pressure is reduced by the first relief valve 31a or the second relief valve 31b, the outlet relief valve 41 can be omitted.
When FIG. 15 and FIG. 16 are compared with each other, the semi automatic manifold with relief valves at the two sides depicted in FIG. 15 is relatively simple. However, adjustment has to be made manually when replacing the gas sources after switching and it is not easy to master the skill. Gas may also be supplied from both sides at the same time, therefore failing the purpose of having one primary bank and one reserve bank at the same time. The automatic manifold with relief valves and solenoid valves at the two sides depicted in FIG. 16 does not require manual operation to attain automatic switching except when gas sources are to be replaced. However, solenoid valves and control means for controlling the solenoid valves have to be installed. Apart from increased costs, there are disadvantages as follows: a. the manifold is electricity dependent; b. it can only be operated if the output pressure is not high and it is not easy to control the solenoid valves if the pressure is high; c. explosion prevention measures have to be caused at flammable work stations and there exist potential safety hazard; d. controls have to be administered at various parts and the failure rate is high.